Parasympathomimetic drug

For a cholinergic agent, the following criteria describe the structure activity relationship: • Ing's Rule of 5: there should be no more than five atoms between the nitrogen and the terminal hydrogen for muscarinic (or cholinergic) activity; • the molecule must possess a nitrogen atom capable of bearing a positive charge, preferably a quaternary ammonium salt; • for maximum potency, the size of the alkyl groups substituted on the nitrogen should not exceed the size of a methyl group; • the molecule should have an oxygen atom, preferably an ester-like oxygen capable of participating in a hydrogen bond; • there should be a two-carbon unit between the oxygen atom and the nitrogen atom. ==Pharmaceuticals/Supplements==

Direct-acting These act by stimulating the nicotinic or muscarinic receptors. • Choline esters • Acetylcholine (all acetylcholine receptors) • Bethanechol (M3 receptors) • Carbachol (all muscarinic receptors and some nicotinic receptors) • Methacholine (all muscarinic receptors) • Plant alkaloids • Arecoline • Nicotine • Muscarine • Pilocarpine (M3 receptors) Indirect-acting Indirect acting parasympathomimetic substances may be either reversible cholinesterase inhibitors, irreversible cholinesterase inhibitors or substances that promote ACh release or anti-adrenergics. The latter inhibits the antagonistic system, the sympathetic nervous system. • Reversible cholinesterase inhibitors • Donepezil • Edrophonium • Neostigmine • Physostigmine • Pyridostigmine • Rivastigmine • Tacrine • Caffeine (non-competitive) • Huperzine A • Irreversible cholinesterase inhibitors • Echothiophate • Isoflurophate • Malathion • ACh release promoters • Alpha GPC • Cisapride • Droperidol • Domperidone • Metoclopramide • Risperidone • Paliperidone • Anti-adrenergics: See also alpha blocker and beta blocker • Clonidine (α-receptor agonist, α2 > α1, giving negative feedback) • Methyldopa (α2 agonist, giving negative feedback) • Propranolol (β-receptor antagonist) • Metoprolol (β-receptor antagonist) • Atenolol (β1 antagonist) • Prazosin (α1 antagonist) • Oxymetazoline (partial α2 adrenergic agonist) ==See also==